Im currently working on a circuit which operates at high currents. The circuit has an LM317 which requires an efficient heat sink for its operation under such conditions.
Please suggest a suitable heat sink ?

Determining a suitable heatsink requires a LOT more information that what you've posted.

Most often, people will shove a heatsink, and, if after X hours of operation, the device hasn't caught fire, it counts as a valid heatsink.

However, the science behind it requires knowledge about maximum operating range, ambient temperature, ambient air speed, how efficient is the convection cooling of the surrounding atmosphere, air density, and many others. There are rule-of thumbs for using heatsinks, but they are not exact, though work well.

So, what is the maximum current you are passing and the duration of that?

In my circuit, the LM 317 operating conditions are,
max. current = 350 mA for a duration of 20 minutes.
ambient temperature = 50 °C.
I need the thermal resistance and the configuration of the heat sink?

In my circuit, the LM 317 operating conditions are,
max. current = 350 mA for a duration of 20 minutes.
ambient temperature = 50 °C.
I need the thermal resistance and the configuration of the heat sink?

FYI: I personally took thermal data for publication on TO-220 and TO-263 and the LOWEST theta J-A value I could obtain soldered to a 10" x 10" copper PCB was about 30C/W. For a small copper "tab" about one square inch it was around 40C/W.

It's a common mistake to believe datatsheets. I guess it was my turn to get fooled.

Click to expand...

Lot of misprints around. Most data sheets are done by marketing guys. I have no idea who screwed up the one you saw.... but I worked at nat Semi where the original version of the LM317 document was written. They are owned by TI now and that data sheet is the TI version. Probably have idiots doing the data sheets. They laid off all the people who knew what was going on there, including me.

That's why I said it was 60C/W ballpark. Different departments at Nat Sem got slightly different values depending on who took the data, it also varies SLIGHTLY depending on die size of the device inside the package. But 60C/W is about right.